A conventional chain saw includes a body and a guide bar that supports the saw chain. A cover clamps the guide bar to the body by means of a tightening arrangement, comprising a bar bolt and a nut. For some reasons, e.g. for changing bars or if the chain has come off, the cover may have to be detached from the body. Before the cover can be detached, the tightening arrangement has to be loosened such that the nut is detached from the bar bolt.
A problem with conventional tightening arrangements, where the nut is loose when detached from the bar bolt, is that an operator of the tool might lose the nut when detaching the cover from the body, especially if situated in a forest. The operator often puts the nut on the ground after detaching it from the bar bolt, and since the ground is usually covered by brushwood and scrub, finding the nut again might be difficult.
An arrangement where the nut is disposed in the interior of the cover, and consequently can't be lost when detaching the cover, is disclosed in US2001/0042311. A disadvantage with this arrangement is that the cover can not be pressed towards the body in order to hold the guide bar in position before starting to thread the nut and the bolt, since the nut will bear against the bolt before the cover bears against the guide bar. Instead the operator has to hold the guide bar in position with one hand while threading the nut with the other hand, which makes the attaching operation complicated.
For large chain saws, having long guide bars, the guide bar tightening arrangement is exposed to greater strain and two bar bolts with corresponding nuts are generally used in order to strengthen the mounting. An arrangement having two bar bolts is disclosed in U.S. Pat. No. 5,497,557. In a chain saw having more than one bar bolt, the arrangement described in US2001/0042311 is not convenient since it would not allow loosening the nuts one at a time. Instead the operator has to unthread the nuts alternately, which makes the detaching of the cover from the body a bit tedious.
There are also other reasons for the operator to detach the cover, not only for the purpose of changing bar or changing chain. For instance, the operator is doing a weekly overhaul that might include inspection of break components and inspection of the centrifugal clutch. The cover needs to be detached during such inspections. A further reason for detaching the cover is for getting access to and cleaning the grove or hole in the bar which provides the chain with chain oil. The groove or hole might become clogged by dirt during long term use in severe operating conditions and is sometimes in need of cleaning.